The present invention relates to a standoff mounting arm for mounting a probe for sensing slow lateral movements of a helicopter, which also mounts one or more additional air data sensing probes or sensors. The mounting arm extends forwardly or sideways from the helicopter body to support a vertically oriented probe in the downward airflow or downwash region below an overhead rotor. The vertically oriented probe has pressure sensing ports spaced around its periphery which all sense equal pressure when the helicopter is hovering but when there is horizontal movement, there are differential pressures sensed at ports on opposite sides of the probe. The standoff mounting arm also can support pitot pressure sensing probes, outside air temperature sensors, ice detectors, and/or total air temperature sensors.
Detecting low air speed on a helicopter is a problem, in that probe sensors that are now used for sensing very low air speeds are generally affected adversely by the downwash flow from the overhead rotor. In a hover mode, the existing probe sensors generally can detect some pressure differentials at higher speeds, but when the aircraft moves laterally very slowly in any direction, the sensors now used are not completely reliable.
Global positioning satellite receivers have been used for detecting lateral movement relative to the ground, but even those devices are incapable of detecting very low speed, such as when a helicopter is hovering and moves slightly horizontally, that is laterally, whether sideways, forwardly or rearwardly.
Global positioning satellite receivers only detect movement relative to an earth based coordinate system. Influences due to wind and helicopter orientation are ignored.
Standoff probes have been used on helicopters with rigid support arms that mount pitot pressure sensors and other air data sensors at outer ends thereof.
The present invention relates to a rigid standoff mounting arm that extends generally forwardly or sideways from the fuselage of a helicopter, and mounts a pressure sensing probe in the downwash of the rotor. The probe has an axis positioned substantially parallel to the axis of rotation of a helicopter rotor, or in other words perpendicular to a reference axis of the helicopter body. The pressure sensor probe in the downwash is provided with a plurality of ports symmetrically spaced around the outer surface of a barrel or tube, which is generally a cylindrical tube. When the helicopter is stationary, the same pressure is sensed at all the ports in the barrel or tube wall around the central axis of the probe, but when the helicopter starts to move laterally, that is sideways, forwardly or rearwardly, differentials in pressure are sensed at selected ports facing in the direction of movement, and compared to pressures sensed at the ports on the opposite side of the probe barrel or tube, and which face in an opposite direction from the direction of movement.
The standoff mounting arm of the present invention also mounts one or more other sensors. These sensors may include pitot pressure sensors, outside air temperature sensors, ice detectors, and total air temperature sensors.